Present technology allows, with frequency multiplexing, 2400 B/S full duplex operation over the switched telephone network. This is accomplished by using 600 baud data transmission on 1200 Hz and 2400 Hz carriers with 16-state modulation, and modems using this technology are typically referred to as V.22 bis modems. The best sample frequency for a digital signal processor implementing this type of modem is 7200 Hz, which is the lowest sample frequency divisible by 2400, with a Nyquist bandwidth greater than 3000 Hz.
With the ever increasing demand for faster data communications, it is desirable to increase the data throughput of modems without using the costly echo cancellation techniques which are conventionally employed in modems of this type to cancel out near and far end echoes of the transmitted signal generated by imperfect hybrids.